Polarizing plate and display apparatus having the same

ABSTRACT

A display apparatus comprises a display panel, a first polarizing plate and a second polarizing plate. The display panel comprises a first substrate including a pixel electrode, a second substrate opposite to the first substrate, and a liquid crystal layer disposed between a first surface of the first substrate and a first surface of the second substrate. The first polarizing plate comprises a first polarizer having a first polarizing axis, and a first λ/4 phase difference plate having a refractive index between about 1.35 and about 2.05 in a thickness direction. The second polarizing plate comprises a second polarizer having a second polarizing axis crossing the first polarizing axis, and a second λ/4 phase difference plate having a refractive index between about 1.35 and about 2.05 in a thickness direction. Accordingly, light leakage in a side view may be reduced and viewing angle may be improved.

PRIORITY STATEMENT

This application claims priority to Korean Patent Application No.10-2009-94226, filed on Oct. 5, 2009, and all the benefits accruingtherefrom under 35 U.S.C. §119, the contents of which are hereinincorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Example embodiments of the present invention relate to flat paneldisplays. More particularly, example embodiments of the presentinvention relate to a flat panel display polarizing plate capable ofimproving display quality and the display apparatus having thepolarizing plate.

2. Description of the Related Art

Liquid crystal displays (LCDs) have seen increasing popularity for theirrelatively small thicknesses, light weight, and low power consumption,making them desirable for use in many different devices, such asmonitors, laptop computers, cellular phones, and so on. Recently, LCDshave also been used in digital information displays (DIDs). The DID is adisplay apparatus commonly used in providing information in publicplaces such as airports, subway stations, shopping malls, theaters, andthe like. The DID may display various digital information similar to aconventional signboard.

The typical LCD apparatus includes an LCD panel displaying imagesaccording to the light transmittance of a liquid crystal, and abacklight assembly disposed under the LCD panel to provide light to theLCD panel.

The typical LCD panel includes a first substrate, a second substrateopposite to the first substrate and having a common electrode, and aliquid crystal layer disposed between the first and second substrates.The liquid crystal has an anisotropic refractive index, so that theliquid crystal induces a phase difference in light generated from thebacklight assembly, where the magnitude of the phase difference dependson the incident angle of the light.

For example, when the LCD apparatus includes the liquid crystal layer ina vertical alignment (VA) mode, incident light that is perpendicular tothe liquid crystal layer passes through the liquid crystal with no phasedifference, but light that is obliquely incident to the liquid crystallayer may have a phase difference imparted. In this manner, LCD panelsoften both refract, and generate a phase difference in non-perpendicularemitted light.

Thus, the amount of light from a side view is different from the amountof light from a front view, so that at some viewing angles, lightleakage occurs. Accordingly, in LCD apparatuses with a liquid crystallayer in VA mode, a contrast ratio (CR) varies in accordance with theviewing angle. For example, the LCD apparatus displays images having ahigh CR in straight-on front views, and images having a low CR in sideviews.

BRIEF SUMMARY OF THE INVENTION

Example embodiments of the present invention provide a polarizing platecapable of improving a viewing angle.

Example embodiments of the present invention provide a display apparatushaving the polarizing plate.

According to one aspect of the present invention, a polarizing platecomprises a polarizer and a λ/4 phase difference plate. The polarizerhas a polarizing axis. The λ/4 phase difference plate is disposed overthe polarizer and has a refractive index between about 1.35 and about2.05 in a thickness direction.

In an example embodiment of the present invention, the polarizing platemay further comprise a compensating film disposed between the polarizerand the λ/4 phase difference plate.

In an example embodiment of the present invention, the compensating filmmay be a positive A-plate, and a phase delay value of the positiveA-plate is between about 70 nm and about 140 nm in a thicknessdirection.

In an example embodiment of the present invention, the compensating filmmay be a negative C-plate, and a phase delay value of the negativeC-plate is between about 30 nm and about 80 nm in a thickness direction.

In an example embodiment of the present invention, the refractive indexmay be between about 1.65 and about 1.75.

According to another aspect of the present invention, a polarizing platecomprises a polarizer, a λ/4 phase difference plate, a positive A-plateand a negative C-plate. The polarizer has a polarizing axis. The λ/4phase difference plate is disposed over the polarizer and has arefractive index between about 1.35 and about 2.05 in a thicknessdirection. The positive A-plate is disposed between the polarizer andthe λ/4 phase difference plate. The negative C-plate is disposed betweenthe positive A-plate and the polarizer.

According to still another aspect of the present invention, a polarizingplate comprises a polarizer, a λ/4 phase difference plate, a positiveA-plate and a negative C-plate. The polarizer has a polarizing axis. Theλ/4 phase difference plate is disposed over the polarizer and has arefractive index between about 1.35 and about 2.05 in a thicknessdirection. The negative C-plate is disposed between the polarizer andthe λ/4 phase difference plate. The positive A-plate is disposed overthe negative C-plate.

According to still another aspect of the present invention, a displayapparatus comprises a display panel, a first polarizing plate and asecond polarizing plate. The display panel comprises a first substrateincluding a pixel electrode, a second substrate opposite to the firstsubstrate, and a liquid crystal layer disposed between a first surfaceof the first substrate and a first surface of the second substrate. Thefirst polarizing plate comprises a first polarizer disposed under asecond surface of the first substrate and having a first polarizing axisand a first λ/4 phase difference plate disposed between the secondsurface of the first substrate and the first polarizer and having arefractive index between about 1.35 and about 2.05 in a thicknessdirection. The second polarizing plate comprises a second polarizerdisposed over a second surface of the second substrate and having asecond polarizing axis crossing the first polarizing axis and a secondλ/4 phase difference plate disposed between the second surface of thesecond substrate and the second polarizer and having refractive indexbetween about 1.35 and about 2.05 in a thickness direction.

In an example embodiment of the present invention, a phase delay valueof the liquid crystal layer may be from about 275 nm to about 350 nm ata wavelength of about 550 nm.

In an example embodiment of the present invention, the first polarizingplate may further comprise a compensating film disposed between thefirst polarizer and the first λ/4 phase difference plate so as tocompensate for a phase difference generated by the liquid crystal layer.

In an example embodiment of the present invention, the refractive indexof at least one of the first λ/4 phase difference plate and the secondλ/4 phase difference plate may be between about 1.65 and about 1.75.

According to still another aspect of the present invention, a displayapparatus comprises a display panel, a first polarizing plate and asecond polarizing plate. The display panel comprises a first substrateincluding a pixel electrode, a second substrate opposite to the firstsubstrate, and a liquid crystal layer disposed between a first surfaceof the first substrate and a first surface of the second substrate. Thefirst polarizing plate comprises a first polarizer disposed under asecond surface of the first substrate and having a first polarizingaxis, a first λ/4 phase difference plate disposed between the secondsurface of the first substrate and the first polarizer and having arefractive index between about 1.35 and about 2.05 in a thicknessdirection, a positive A-plate disposed between the first polarizer andthe first λ/4 phase difference plate and a negative C-plate disposedbetween the first polarizer and the first λ/4 phase difference plate.The second polarizing plate comprises a second polarizer disposed over asecond surface of the second substrate and having a second polarizingaxis crossing the first polarizing axis and a second λ/4 phasedifference plate disposed between the second surface of the secondsubstrate and the second polarizer and having refractive index betweenabout 1.35 and about 2.05 in a thickness direction.

In an example embodiment of the present invention, the positive A-platemay be disposed over the first polarizer. The negative C-plate may bedisposed over the positive A-plate.

In an example embodiment of the present invention, the negative C-platemay be disposed over the first polarizer. The positive A-plate may bedisposed over the negative C-plate.

In an example embodiment of the present invention, the refractive indexof at least one of the first λ/4 phase difference plate and the secondλ/4 phase difference plate may be between about 1.65 and about 1.75.

According to the present invention, first and second λ/4 phasedifference plates are disposed over and under a display panel andrefractive indexes of the first and second λ/4 phase difference platesin thickness directions are adjusted so that light leakage in a sideview may be decreased. This results in improved viewing angle of thedisplay apparatus.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detailed example embodimentsthereof with reference to the accompanying drawings, in which:

FIG. 1 is a cross sectional view illustrating a display apparatusaccording to an example embodiment of the present invention;

FIG. 2 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 1;

FIGS. 3A to 3G are graphs illustrating a luminance distribution withrespect to the refractive index of first and second λ/4 phase differenceplates of FIG. 1 in thickness directions;

FIG. 4 is a graph illustrating a viewing angle with respect to therefractive index of first and second λ/4 phase difference plates of FIG.1 in thickness directions;

FIGS. 5A and 5B are graphs illustrating a contrast ratio (CR) withrespect to a refractive index of first and second λ/4 phase differenceplates of FIG. 1 in thickness directions;

FIG. 6 is a cross sectional view illustrating a display apparatusaccording to another example embodiment of the present invention;

FIG. 7 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 6;

FIG. 8 is a graph illustrating a configuration of a positive A-plate ofFIG. 7;

FIGS. 9A to 9H are graphs illustrating a luminance distribution withrespect to phase delay of a positive A-plate of FIG. 6 in a thicknessdirection;

FIG. 10 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention;

FIG. 11 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 10;

FIGS. 12A to 12C are graphs illustrating a luminance distribution withrespect to phase delay of a negative C-plate of FIG. 10 in a thicknessdirection;

FIG. 13 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention;

FIG. 14 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 13;

FIG. 15 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention;

FIG. 16 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention;

FIG. 17 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention;

FIG. 18 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention;and

FIG. 19 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 18.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described more fully hereinafter with referenceto the accompanying drawings, in which exemplary embodiments of thepresent invention are shown. The present invention may, however, beembodied in many different forms and should not be construed as limitedto the exemplary embodiments set fourth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the present invention tothose skilled in the art. In the drawings, the sizes and relative sizesof layers and regions may be exaggerated for clarity.

It will be understood that when an element or layer is referred to asbeing “on” or “connected to” another element or layer, it can bedirectly on or connected to the other element or layer or interveningelements or layers may be present. In contrast, when an element isreferred to as being “directly on” or “directly connected to” anotherelement or layer, there are no intervening elements or layers present.Like numerals refer to like elements throughout. As used herein, theterm “and/or” includes any and all combinations of one or more of theassociated listed items.

It will be understood that, although the terms first, second, third,etc. may be used herein to describe various elements, components,regions, layers and/or sections, these elements, components, regions,layers and/or sections should not be limited by these terms. These termsare only used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

Spatially relative terms, such as “lower,” “upper” and the like, may beused herein for ease of description to describe one element or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. It will be understood that the spatially relative terms areintended to encompass different orientations of the apparatus in use oroperation in addition to the orientation depicted in the figures. Forexample, if the apparatus in the figures is turned over, elementsdescribed as “lower” other elements or features would then be oriented“upper” the other elements or features. Thus, the exemplary term “lower”can encompass both an orientation of above and below. The apparatus maybe otherwise oriented (rotated 90 degrees or at other orientations) andthe spatially relative descriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularexemplary embodiments only and is not intended to be limiting of thepresent invention. As used herein, the singular forms “a,” “an” and“the” are intended to include the plural forms as well, unless thecontext clearly indicates otherwise. It will be further understood thatthe terms “comprises” and/or “comprising,” when used in thisspecification, specify the presence of stated features, integers, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Exemplary embodiments of the invention are described herein withreference to cross sectional illustrations that are schematicillustrations of idealized example embodiments (and intermediatestructures) of the present invention. As such, variations from theshapes of the illustrations as a result, for example, of manufacturingtechniques and/or tolerances, are to be expected. Thus, exemplaryembodiments of the present invention should not be construed as limitedto the particular shapes of regions illustrated herein but are toinclude deviations in shapes that result, for example, frommanufacturing.

For example, an implanted region illustrated as a rectangle will,typically, have rounded or curved features and/or a gradient of implantconcentration at its edges rather than a binary change from implanted tonon implanted region. Likewise, a buried region formed by implantationmay result in some implantation in the region between the buried regionand the surface through which the implantation takes place. Thus, theregions illustrated in the figures are schematic in nature and theirshapes are not intended to illustrate the actual shape of a region of anapparatus and are not intended to limit the scope of the presentinvention.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

All methods described herein can be performed in a suitable order unlessotherwise indicated herein or otherwise clearly contradicted by context.The use of any and all examples, or exemplary language (e.g., “suchas”), is intended merely to better illustrate the invention and does notpose a limitation on the scope of the invention unless otherwiseclaimed. No language in the specification should be construed asindicating any non-claimed element as essential to the practice of theinvention as used herein.

Embodiments of the invention utilize display panels that employ at leastone λ/4 phase difference plate and polarizer. In addition to acting ascircular polarizers, the one or more λ/4 phase difference plates eachhave a specified refractive index. When the values of these refractiveindices are chosen correctly, light leakage of the display panel isreduced. In addition to the λ/4 phase difference plates, the displaypanels can also employ one or more compensating films with specifiedphase delays. If the phase delay is chosen correctly, light leakage canbe further reduced, and be made more symmetric.

Hereinafter, the present invention will be explained in detail withreference to the accompanying drawings.

FIG. 1 is a cross sectional view illustrating a display apparatusaccording to an exemplary embodiment of the present invention.

Referring to FIG. 1, the display apparatus according to the presentinvention includes a display panel 100, a first polarizing plate 200, asecond polarizing plate 300 and a backlight unit 400.

The display panel 100 includes a first substrate 110, a second substrate130 opposite to the first substrate 110, and a liquid crystal layer 140disposed between the first substrate 110 and the second substrate 130.

The first substrate 110 further includes a pixel electrode 120. Thepixel electrode 120 is disposed in a pixel area defined by a gate line(not shown) and a data line (not shown) crossing each other. The pixelarea includes a reflective area RA and a transmissive area TA. The pixelelectrode 120 includes a reflective electrode 122 and a transparentelectrode 124. The reflective electrode 122 is disposed in thereflective area RA and includes a conductive reflective material. Thetransparent electrode 124 is disposed in the transmissive area TA andincludes a transparent conductive material. The first substrate 110includes a first surface 111 facing the liquid crystal layer 140 and asecond surface 112 opposite to the first surface 111.

The second substrate 130 includes a plurality of color filters (notshown) and a common electrode (not shown) disposed on the color filters.The color filters may include red color filters, green color filters andblue color filters, or any other desired group of colors. The commonelectrode includes a transparent conductive material. A common voltageis applied to the common electrode. The second substrate 130 includes afirst surface 131 facing the liquid crystal layer 140 and a secondsurface 132 opposite to the first surface 131.

The liquid crystal layer 140 is disposed between the first surface 111of the first substrate 110 and a first surface 131 of the secondsubstrate 130. The liquid crystal layer 140 may be driven in a verticalalignment (VA) mode. The liquid crystal layer 140 includes a pluralityof liquid crystal molecules 142. The liquid crystal molecules 142 arealigned substantially perpendicular to the first and second substrates110 and 130. When an electric field is applied, the liquid crystalmolecules 142 may be aligned substantially parallel with the first andsecond substrates 110 and 130.

The first polarizing plate 200 is attached to the second surface 112 ofthe first substrate 110. The first polarizing plate 200 may include afirst protection layer 210, a first polarizer 220 and a first λ/4 phasedifference plate 230.

The first protection layer 210 is disposed under the first polarizer 220so that the first protection layer 210 protects the first polarizer 220.The first protection layer 210 may include a material having durabilityand a non-optical configuration. For example, the first protection layer210 may include a tri-acetyl cellulose (TAC) film.

The first polarizer 220 is disposed over the first protection layer 210.For example, the first polarizer 220 may include poly vinyl alcohol(PVA) and a dichromatic material such as iodine (I₂) and chlorine (Cl₂)polarizing light to a specific direction in PVA.

The first λ/4 phase difference plate 230 is disposed between the firstsubstrate 110 and the first polarizer 220. The first λ/4 phasedifference plate 230 delays the light incident from the first polarizer220 by a λ/4 phase. The first λ/4 phase difference plate 230 may have arefractive index nz between about 1.35 and about 2.05 in a thicknessdirection.

The first protection layer 210, the first polarizer 220 and the firstλ/4 phase difference plate 230 may be attached to one another by anadhesive material (not shown).

The second polarizing plate 300 is attached on the display panel 100.The second polarizing plate 300 may include a low-reflective film 310, asecond protection layer 320, a second polarizer 330, and a second λ/4phase difference plate 340.

The low-reflective film 310 is disposed over the second protection layer320. The low-reflective film 310 includes a material having relativelylow refractivity, so that the low-reflective film 310 reduces areflective ratio of external light a. The reflective ratio of thelow-reflective film 310 may be less than about 1%. Accordingly, glare bythe reflection may be largely prevented.

The second protection layer 320 is disposed over the second polarizer330 so that the second protection layer 320 protects the secondpolarizer 330. The second protection layer 320 may include a TAC film.

The second polarizer 330 is disposed under the second protection layer320. For example, the second polarizer 330 may include poly vinylalcohol (PVA) and a dichromatic material such as I₂ and/or Cl₂,polarizing the light according to a specific direction in the PVA.

The second λ/4 phase difference plate 340 is disposed between the secondsubstrate 130 and the second polarizer 330. The second λ/4 phasedifference plate 340 delays the light incident from the second substrate130 by λ/4. The second λ/4 phase difference plate 340 may have arefractive index nz between about 1.35 and about 2.05 in a thicknessdirection.

The low-reflective film 310, the second protection layer 320, the secondpolarizer 330 and the second λ/4 phase difference plate 340 may beattached to one another by one or more adhesive materials (not shown).

The backlight unit 400 is disposed under the first polarizing plate 200.A generated light b from the backlight unit 400 is transmitted throughthe first polarizing plate 200, the display panel 100 and the secondpolarizing plate 300 in sequence, so that images are displayed.

FIG. 2 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 1.

Referring to FIGS. 1 and 2, the first polarizer 220 has a firstabsorptive axis 220 a substantially parallel to a first direction D1,and a first polarizing axis 220 b substantially parallel to a seconddirection D2. Here, second direction D2 is substantially perpendicularto the first direction D1. The first polarizer 220 includes a firstsurface 221 and a second surface 222 opposite to the first surface 221.

The first λ/4 phase difference plate 230 is disposed between the firstsurface 221 of the first polarizer 220 and the second surface 112 of thefirst substrate 110. The first λ/4 phase difference plate 230 includes afirst surface 231 facing the first surface 221 of the first polarizer220, and a second surface 232 facing the second surface 112 of the firstsubstrate 110. The first λ/4 phase difference plate 230 has a firstdelaying axis 230 a inclined by an angle of about 45 degrees or about135 degrees with respect to the first polarizing axis 220 b of the firstpolarizer 220.

The display panel 100 includes first substrate 110, second substrate130, and liquid crystal layer 140 disposed between the first substrate110 and the second substrate 130. A phase delay value Δnd of the liquidcrystal layer 140 may be from about 275 nm to about 350 nm at awavelength of about 550 nm. For example, the phase delay value Δnd ofthe liquid crystal layer 140 may be about 325 nm. The Δn is ananisotropic refractive index of the liquid crystal layer 140 and d is acell gap of the liquid crystal layer 140.

The second λ/4 phase difference plate 340 is disposed over the displaypanel 100. In detail, the second λ/4 phase difference plate 340 isdisposed over the second surface 132 of the second substrate 130. Thesecond λ/4 phase difference plate 340 includes a first surface 341facing the second surface 132 of the second substrate 130, and a secondsurface 342 facing the first surface 331 of the second polarizer 330.The second λ/4 phase difference plate 340 has a second delaying axis 340a substantially perpendicular to the first delaying axis 230 a. Thesecond delaying axis 340 a is inclined by an angle of about 45 degrees,or about 135 degrees with respect to a second polarizing axis 330 b ofthe second polarizer 330.

The first and second λ/4 phase difference plates 230 and 340 may have arefractive index nz between about 1.35 and about 2.05 in a thicknessdirection corresponding to the liquid crystal layer 140, with acorresponding phase delay value Δnd of about 275 nm to about 350 nm at awavelength of about 550 nm.

The second polarizer 330 is disposed over the second surface 342 of thesecond λ/4 phase difference plate 340. The second polarizer 330 has asecond absorptive axis 330 a substantially perpendicular to the firstabsorptive axis 220 a, and a second polarizing axis 330 b substantiallyperpendicular to the second absorptive axis 330 a.

The above-described structure helps reduce reflection of the externallight a from the surface of the display panel 100. For example, bypassing through the second polarizer 330, the external light a islinearly polarized substantially parallel with the second polarizingaxis 330 b of the second polarizer 330. The linearly polarized light isconverted to circularly polarized light by the second λ/4 phasedifference plate 340. The circularly polarized light then falls incidentto the display panel, where it is reflected by the surface of thedisplay panel 100. The reflected light is polarized linearly, andentirely blocked by the second polarizer 330. Therefore, glare due toreflection of external light a is reduced by the presence of the secondλ/4 phase difference plate 340.

The display panel 100 may be driven in reflective mode or transmissivemode. That is, the invention encompasses both driving modes.

First, when the display panel 100 is driven in reflective mode, externallight a passes through the second polarizer 330 and the second λ/4 phasedifference plate 340, thus becoming circularly polarized. The externallight a is then incident to the display panel 100. When a voltage is notapplied to the liquid crystal layer 140, the liquid crystal molecules142 of the liquid crystal layer 140 are aligned substantiallyperpendicular to the first and second substrates 110 and 130, so thatthe circularly polarized light simply passes through the liquid crystallayer 140 without any modification. The circularly polarized lightpassing through the liquid crystal layer 140 is then reflected by thereflective electrode 122 and converted to linearly polarized light bythe second λ/4 phase difference plate 340. The axis of the linearlypolarized light is substantially parallel with the second absorptiveaxis 330 a of the second polarizer 330, so that the linearly polarizedlight is absorbed by the second polarizer 330. The display panel 100thus displays black.

In contrast, when a voltage is applied to the liquid crystal layer 140,the liquid crystal molecules 142 of the liquid crystal layer 140 arealigned substantially parallel with the first and second substrates 110and 130, so that the circularly polarized light passing through theliquid crystal layer 140 is converted to linearly polarized light. Thelinearly polarized light is then reflected by the reflective electrode122. By passing through the liquid crystal layer 140 again, the linearlypolarized light is converted to circularly polarized light. Thiscircularly polarized light is converted to linearly polarized light bythe second λ/4 phase difference plate 340, and transmitted through thesecond polarizer 330. The display panel 100 thus displays white.

Second, when the display panel 100 is driven in transmissive mode,generated light b from backlight unit 400 passes through the firstpolarizer 220 and the first λ/4 phase difference plate 230, and isconverted to circularly polarized light. The circularly polarized lightis applied to the display panel 100, where it is applied to the liquidcrystal layer 140 via the transparent electrode 124. When a voltage isnot applied to the liquid crystal layer 140, the liquid crystalmolecules 142 of the liquid crystal layer 140 are aligned substantiallyperpendicular to the first and second substrates 110 and 130, so thatthe circularly polarized light simply passes through the liquid crystallayer 140 without any modification. The circularly polarized light isthen converted to linearly polarized light by the second λ/4 phasedifference plate 340. The axis of the linearly polarized light issubstantially parallel with the second absorptive axis 330 a of thesecond polarizer 330, so that the linearly polarized light is absorbedby the second polarizer 330. The display panel 100 thus displays black.

Alternatively, when a voltage is applied to the liquid crystal layer140, the liquid crystal molecules 142 of the liquid crystal layer 140are aligned substantially parallel with the first and second substrates110 and 130, so that the circularly polarized light passing through theliquid crystal layer 140 is converted to linearly polarized light. Thelinearly polarized light is converted to circularly polarized light bythe second λ/4 phase difference plate 340, and transmitted through thesecond polarizer 330. The display panel 100 thus displays white.

FIGS. 3A to 3G are graphs illustrating luminance distribution of displaypanel 100 when black images are displayed as functions of the refractiveindices of the first and second λ/4 phase difference plates of FIG. 1 inthickness directions.

FIG. 3A illustrates the luminance distribution when the phase delayvalue Δnd of the liquid crystal layer 140 is about 325 nm at awavelength of about 550 nm, and the refractive index nz of the first andsecond λ/4 phase difference plates 230 and 340 is about 1.35 inthickness directions. FIG. 3B illustrates the luminance distributionwhen the phase delay value Δnd of the liquid crystal layer 140 is about325 nm at a wavelength of about 550 nm, and the refractive index nz ofthe first and second λ/4 phase difference plates 230 and 340 is about1.45 in thickness directions.

Referring to FIGS. 3A and 3B, when a polar angle θ is between about 0and about 20 degrees, the luminance was very low (for example, about0.000 cd/m²) for every azimuth angle φ. This indicates that there is nolight leakage when black images are displayed. The azimuth angle φ is arotating angle with respect to a specific axis when light transmits toan incident surface, and the polar angle θ is an angle of inclinationwith respect to a normal of the incident face. The luminance increasesas the polar angle θ increases. In particular, the luminance is about0.015 cd/m² to about 0.020 cd/m² in four different orientations: when 1)the polar angle θ is about 60 degrees and the azimuth angle φ is betweenabout 0 and about 30 degrees, 2) the polar angle θ is about 60 degreesand the azimuth angle φ is between about 90 and about 120 degrees, 3)the polar angle θ is about 60 degrees and the azimuth angle φ is betweenabout 180 and about 210 degrees, and 4) the polar angle θ is about 60degrees and the azimuth angle φ is between about 270 and about 300degrees. The luminance value for these four orientations indicates thatlight leakage occurs at these orientations. From FIGS. 3A and 3B, it canalso be seen that reducing the refractive index nz of the first andsecond λ/4 phase difference plates 230 and 340 from about 1.45 to about1.35 reduces light leakage.

FIG. 3C illustrates the luminance distribution when the phase delayvalue Δnd of the liquid crystal layer 140 is about 325 nm at awavelength of about 550 nm, and the refractive index nz of the first andsecond λ/4 phase difference plates 230 and 340 is about 1.55 inthickness directions. FIG. 3D illustrates the luminance distributionwhen the phase delay value Δnd of the liquid crystal layer 140 is about325 nm at a wavelength of about 550 nm, and the refractive index nz ofthe first and second λ/4 phase difference plates 230 and 340 is about1.65 in thickness directions. FIG. 3E illustrates the luminancedistribution when the phase delay value Δnd of the liquid crystal layer140 is about 325 nm at a wavelength of about 550 nm, and the refractiveindex nz of the first and second λ/4 phase difference plates 230 and 340is about 1.75 in thickness directions. FIG. 3F illustrates the luminancedistribution when the phase delay value Δnd of the liquid crystal layer140 is about 325 nm at a wavelength of about 550 nm, and the refractiveindex nz of the first and second λ/4 phase difference plates 230 and 340is about 1.85 in thickness directions.

Referring to FIGS. 3C to 3F, when the refractive index nz of the firstand second λ/4 phase difference plates 230 and 340 is between about 1.55and about 1.85 in thickness directions, the “overall” luminance wasgenerally reduced (for example, no more than about 0.010 cd/m²) relativeto that of FIGS. 3A and 3B. That is, light leakage is reduced.

FIG. 3G illustrates the luminance distribution when the phase delayvalue Δnd of the liquid crystal layer 140 is about 325 nm at awavelength of about 550 nm, and the refractive index nz of the first andsecond λ/4 phase difference plates 230 and 340 is about 2.05 inthickness directions. Referring to FIG. 3G, the luminance increases asthe polar angle θ increases. In particular, the luminance increases tovalues of about 0.015 cd/m² to about 0.020 cd/m² in four cases, ororientations: when 1) the polar angle θ is about 60 degrees and theazimuth angle φ is between about 30 and about 60 degrees, 2) the polarangle θ is about 60 degrees and the azimuth angle φ is between about 120and about 150 degrees, 3) the polar angle θ is about 60 degrees and theazimuth angle φ is between about 210 and about 240 degrees, and 4) thepolar angle θ is about 60 degrees and the azimuth angle φ is betweenabout 300 and about 330 degrees. Accordingly, light leakage occurs atthese four orientations.

As shown in the above FIGS. 3A-3G, the “overall” luminance distributionsare lowest for refractive indices nz between 1.65 and 1.75 (i.e., FIGS.3D-3E). That is, for the above-described configuration, light leakage isminimized when the first and second λ/4 phase difference plates 230 and340 have refractive indices nz between 1.65 and 1.75. However, theseresults are specific to a phase delay value Δnd of the liquid crystallayer 140 being about 325 nm at a wavelength of about 550 nm. Theresults may be different for different conditions.

FIG. 4 is a graph illustrating a viewing angle with respect torefractive index of the first and second λ/4 phase difference plates ofFIG. 1 in thickness directions.

In FIG. 4, an X axis represents a polar angle and a Y axis representsluminance.

A luminance curve D11 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.45in thickness directions, and the azimuth angle φ is about 0 degrees. Aluminance curve D12 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.45in thickness directions, and the azimuth angle φ is about 45 degrees. Aluminance curve D21 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.55in thickness directions, and the azimuth angle φ is about 0 degrees. Aluminance curve D22 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.55in thickness directions, and the azimuth angle φ is about 45 degrees. Aluminance curve D31 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.65in thickness directions, and the azimuth angle φ is about 0 degrees. Aluminance curve D32 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.65in thickness directions, and the azimuth angle φ is about 45 degrees. Aluminance curve D41 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.75in thickness directions, and the azimuth angle φ is about 0 degrees. Aluminance curve D42 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.75in thickness directions, and the azimuth angle φ is about 45 degrees. Aluminance curve D51 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.85in thickness directions, and the azimuth angle φ is about 0 degrees. Aluminance curve D52 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.85in thickness directions, and the azimuth angle φ is about 45 degrees. Aluminance curve D61 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 2.05in thickness directions, and the azimuth angle φ is about 0 degrees. Aluminance curve D62 is measured when the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 2.05in thickness directions, and the azimuth angle φ is about 45 degree.

As shown in the above curves, when the refractive index nz of the firstand second λ/4 phase difference plates 230 and 340 is about 1.65 inthickness directions, the luminance remains relatively low for any valueof polar angle θ. For example, as shown in the luminance curve D31, theluminance reaches a maximum of about 0.004 cd/m² when the azimuth angleφ is about 0 degrees and the polar angle θ is about 60 degrees.Similarly, with respect to curve D32, the luminance reaches a maximum ofabout 0.007 cd/m² when the azimuth angle φ is about 45 degrees and thepolar angle θ is about 60 degrees. There is substantially no lightleakage in both frontal and extreme side views of the display panel 100(i.e., when θ is almost zero or almost 90 degrees).

One can also see that, when refractive index nz is less than or equal toabout 1.65, azimuth angle φ does not have a strong effect on luminance.However, when refractive index nz exceeds 1.65, luminance begins to varywith φ to a much greater extent. For example, with reference to curvesD61 and D62 (i.e., for nz=2.05), luminance reaches a maximum of onlyabout 0.001 cd/m² when the azimuth angle φ is about 0 degrees, butreaches a maximum of about 0.018 cd/m² when the azimuth angle φ is about45 degrees. These results also show that light leakage occurspredominantly at intermediate viewing angles of the display panel 100,with maximum light leakage occurring at a viewing angle of approximately60 degrees.

As shown above, when the refractive index nz of the first and second λ/4phase difference plates 230 and 340 is between about 1.55 and about 1.75in thickness directions, the overall luminance is relatively low, anddoes not vary much from front view to side view. That is, when the phasedelay value Δnd of the liquid crystal layer 140 is about 325 nm at awavelength of about 550 nm, and the refractive index nz of the first andsecond λ/4 phase difference plates 230 and 340 is between about 1.55 andabout 1.75 in thickness directions, light leakage is kept to a relativeminimum. However, these results are specific to a phase delay value Δndof the liquid crystal layer 140 that is about 325 nm at a wavelength ofabout 550 nm. Results may differ for other phase delay values.

FIGS. 5A and 5B are graphs illustrating a contrast ratio (CR) withrespect to the refractive index nz of the first and second λ/4 phasedifference plates of FIG. 1 in thickness directions.

FIG. 5A is a graph illustrating a CR with respect to the refractiveindex of the first and second λ/4 phase difference plates, at ahorizontal viewing angle. The phase delay value Δnd of the liquidcrystal layer 140 is about 325 nm.

For example, curve A1 represents the CR measured when the azimuth angleφ is about 0 degrees and the polar angle θ is about −60 degrees. Whenthe refractive index nz of the first and the second λ/4 phase differenceplates 230 and 340 is about 1.4 in thickness directions, the CR is about9.9.

When the refractive index nz is about 1.5 in a thickness direction, theCR is about 11.4. When the refractive index nz of the first and thesecond λ/4 phase difference plates 230 and 340 is about 1., the CR isabout 18.9, and when the refractive index nz is about 1.7, the CR isabout 24.0. When the refractive index nz is about 1.8, the CR is about33.9.

The curve A2 represents the CR measured when the azimuth angle φ isabout 0 degrees and the polar angle θ is about 60 degrees. When therefractive index nz of the first and the second λ/4 phase differenceplates 230 and 340 is about 1.4 in thickness direction, the CR is about11.9. When the refractive index nz is about 1.5, the CR is about 12.7.When the refractive index nz is about 1.6, the CR is about 21.9, andwhen the refractive index nz is about 1.7, the CR is about 27.0. Whenthe refractive index nz is about 1.8 in a thickness direction, the CR isabout 38.0.

FIG. 5B is a graph illustrating a CR with respect to a refractive indexnz of first and second λ/4 phase difference plates in thicknessdirections, at a diagonal viewing angle.

For example, curve B1 represents the CR measured when the azimuth angleφ is about 45 degrees and the polar angle θ is about −60 degrees. Whenthe refractive index nz of the first and the second λ/4 phase differenceplates 230 and 340 is about 1.4 in thickness directions, the CR is about11.0. When the refractive index nz of the first and the second λ/4 phasedifference plates 230 and 340 is about 1.5, the CR is about 10.8. Whenthe refractive index nz is about 1.6, the CR is about 10.6; when therefractive index nz is about 1.7, the CR is about 7.8, and when therefractive index nz is about 1.8 in, the CR is about 6.6.

The curve B2 represents the CR measured when the azimuth angle φ isabout 45 degrees and the polar angle θ is about 60 degrees. When therefractive index nz of the first and the second λ/4 phase differenceplates 230 and 340 is about 1.4 in thickness directions, the CR is about11.6; when the refractive index nz is about 1.5, the CR is about 11.1.When the refractive index nz is about 1.6, the CR is about 10.8; whenthe refractive index nz is about 1.7, the CR is about 8.2; and when therefractive index nz is about 1.8, the CR is about 7.0.

As shown in the above curves, at a horizontal viewing angle, the CRincreases as the refractive index nz of the first and the second λ/4phase difference plates 230 and 340 increases. However, at a diagonalviewing angle, the CR decreases as the refractive index nz increases.

As mentioned above, the CR at a horizontal viewing angle behaves inroughly opposite manner to the CR at a diagonal viewing angle. Choosinga value of refractive index nz thus involves a trade-off between imagequality at different viewing angles. For example, if the horizontalviewing angle is deemed more important, the CR is most preferable whenthe refractive index nz is about 1.8. However, if the diagonal viewingangle is deemed more important, the CR is most preferable when therefractive index nz is about 1.65.

According to the present example embodiment, the low-reflective film 310is disposed over the second polarizer 330, and the second λ/4 phasedifference plate 340 is disposed between the second polarizer 330 andthe second substrate 130, so that glare from reflection of externallight a may be prevented. In addition, the first and second λ/4 phasedifference plates 230 and 340 are disposed, respectively, under and overthe display panel 100, and refractive indexes of the first and secondλ/4 phase difference plates 230 and 340 are adjusted so that lightleakage at a side view may be reduced. This serves to improve theviewing angle of the display apparatus.

FIG. 6 is a cross sectional view illustrating a display apparatusaccording to another example embodiment of the present invention. FIG. 7is a conceptual diagram illustrating an optical operation of the displayapparatus of FIG. 6.

The display apparatus of this embodiment is in many respects the same asthe previous example embodiment of FIG. 1, except that a firstpolarizing plate 200 further includes a positive A-plate 240 as acompensating film. Thus, any repetitive explanation concerning the sameor like elements as those described in the previous example embodimentof FIG. 1 is omitted.

Referring to FIGS. 6 and 7, the first polarizing plate 200 includes afirst protective layer 210, a first polarizer 220, a first λ/4 phasedifference plate 230, and positive A-plate 240. The second polarizingplate 300 includes a low-reflective film 310, a second protective layer320, a second polarizer 330 and a second λ/4 phase difference plate 340.

The first polarizer 220 is disposed between the first protection layer210 and the positive A-plate 240. The first polarizer 220 has a firstabsorptive axis 220 a substantially parallel with a first direction D1and a first polarizing axis 220 b substantially parallel with a seconddirection D2. Here, direction D2 is substantially perpendicular todirection D1. The first polarizer 220 includes a first surface 221, anda second surface 222 that is opposite to the first surface 221.

The positive A-plate 240 is disposed over the first surface 221 of thefirst polarizer 220. The positive A-plate 240 includes a compensatingaxis 240 a substantially parallel with the first polarizing axis 220 b.The positive A-plate 240 includes a first surface 241 facing the firstsurface 221 of the first polarizer 220, and a second surface 242opposite to the first surface 241 of the positive A-plate 240.

A phase delay value Rth of the positive A-plate 240 may be from about 70nm to about 140 nm in a thickness direction. The phase delay value Rthof the positive A-plate in a thickness direction 240 is{(nx+ny)/2−nz}*d. The nx is a refractive index in an x direction, the nyis a refractive index in a y direction that is substantiallyperpendicular to the x direction, and the nz is a refractive index in az direction substantially perpendicular to both x and y directions.Here, d represents a thickness of the positive A-plate 240.

FIG. 8 is a graph illustrating a configuration of a positive A-plate ofFIG. 7.

Referring to FIG. 8, a first positive plane dispersion delay value Ro1is defined as a ratio between a plane phase delay value Ro at awavelength of green light and a plane phase delay value Ro at awavelength of blue light. Here, the first positive plane dispersiondelay value Ro1 is about 1.013, where the wavelength of green light isabout 550 nm and the wavelength of blue light is about 450 nm.

A second positive plane dispersion delay value Ro2 is defined as a ratiobetween the plane phase delay value Ro at a wavelength of green lightand a plane phase delay value Ro at a wavelength of red light. Here, thesecond positive plane dispersion delay value Ro2 is about 0.996, and thewavelength of red light is about 650 nm.

A first positive thickness dispersion delay value Rth1 is defined as aratio between a phase delay value Rth at a wavelength of green light anda phase delay value Rth at the wavelength of blue light. The firstpositive thickness dispersion delay value Rth1 is about 1.011 and issubstantially the same as the first positive plane dispersion delayvalue Ro1.

A second positive thickness dispersion delay value Rth2 is defined as aratio between the phase delay value Rth at a wavelength off green light,and a phase delay value Rth at a wavelength of red light. The secondpositive thickness dispersion delay value Rth2 is about 0.998, and issubstantially the same as the second positive plane dispersion delayvalue Ro2.

Referring back to FIG. 7, the first λ/4 phase difference plate 230 isdisposed over the second surface 242 of the positive A-plate 240. Thefirst λ/4 phase difference plate 230 has a first delaying axis 230 ainclined by an angle of about 45 degrees, or about 135 degrees withrespect to the first polarizing axis 220 b of the first polarizer 220.The first λ/4 phase difference plate 230 includes a first surface 231facing the second surface 242 of the positive A-plate 240, and a secondsurface 232 opposite to the first surface 231. The second surface 232 ofthe first λ/4 phase difference plate 230 is coupled to second surface112 of a first substrate 110.

A display panel 100 includes the first substrate 110, a second substrate130, and a liquid crystal layer 140 disposed between the first substrate110 and the second substrate 130. A phase delay value Δnd of the liquidcrystal layer 140 may be from about 275 nm to about 350 nm at awavelength of about 550 nm. For example, the phase delay value Δnd ofthe liquid crystal layer 140 may be about 325 nm. The Δn is anisotropicrefractive index of the liquid crystal layer 140 and d is a cell gap ofthe liquid crystal layer 140.

The second λ/4 phase difference plate 340 is disposed over the displaypanel 100. In detail, the second λ/4 phase difference plate 340 isdisposed over a second surface 132 of the second substrate 130. Thesecond λ/4 phase difference plate 340 has a second delaying axis 340 asubstantially perpendicular to the first delaying axis 230 a. The seconddelaying axis 340 a is inclined by an angle of about 45 degrees, orabout 135 degrees with respect to a second polarizing axis 330 b of thesecond polarizer 330. The second λ/4 phase difference plate 340 includesa first surface 341 facing the second surface 132 of the secondsubstrate 130, and a second surface 342 opposite to the first surface341 of the second λ/4 phase difference plate 340. The second surface 342of the second λ/4 phase difference plate 340 faces a first surface 331of the second polarizer 330.

For the above-described liquid crystal layer 140 with phase delay valueΔnd of about 275 nm to about 350 nm at a wavelength of about 550 nm, thefirst and second λ/4 phase difference plates 230 and 340 may have arefractive index nz between about 1.35 and about 2.05 in thicknessdirections.

The second polarizer 330 is disposed over the second surface 342 of thesecond λ/4 phase difference plate 340. The second polarizer 330 has asecond absorptive axis 330 a substantially perpendicular to the firstabsorptive axis 220 a, and a second polarizing axis 330 b substantiallyperpendicular to the second absorptive axis 330 a. The second protectivelayer 320 is attached to the second surface 332 of the second polarizer330.

FIGS. 9A to 9H are graphs illustrating a luminance distribution withrespect to phase delay of a positive A-plate of FIG. 6 in a thicknessdirection.

FIG. 9A illustrates a luminance distribution for black images when thephase delay value Δnd of the liquid crystal layer 140 is about 325 nm ata wavelength of about 550 nm, the refractive index nz of the first andsecond λ/4 phase difference plates 230 and 340 is about 1.35 inthickness directions, and the phase delay value Rth of the positiveA-plate 240 is about 70 nm in a thickness direction.

In this example embodiment, “light leakage” is considered to be presentonly if the luminance is more than about 0.015 cd/m².

Referring to FIG. 9A, when the polar angle θ is about 60 degrees and theazimuth angle φ is between about 0 and about 30 degree, and when thepolar angle θ is about 60 degrees and the azimuth angle φ is betweenabout 180 and about 210 degrees, the luminance is about 0.015 cd/m² toabout 0.020 cd/m² and light leakage is considered to occur. However, incomparison to the previous example embodiment of FIG. 3A which does notemploy a compensating film, when the azimuth angle φ is between about 90and about 120 degrees and between about 270 and about 300 degrees, lightleakage is reduced.

FIG. 9B illustrates a luminance distribution when the phase delay valueΔnd of the liquid crystal layer 140 is about 325 nm at a wavelength ofabout 550 nm, the refractive index nz of the first and second λ/4 phasedifference plates 230 and 340 is about 1.35 in thickness directions, andthe phase delay value Rth of the positive A-plate 240 is about 80 nm ina thickness direction. FIG. 9C illustrates a luminance distribution whenthe phase delay value Δnd of the liquid crystal layer 140 is about 325nm at a wavelength of about 550 nm, the refractive index nz of the firstand second λ/4 phase difference plates 230 and 340 is about 1.35 inthickness directions, and the phase delay value Rth of the positiveA-plate 240 is about 90 nm in a thickness direction. FIG. 9D illustratesa luminance distribution when the phase delay value Δnd of the liquidcrystal layer 140 is about 325 nm at a wavelength of about 550 nm, therefractive index nz of the first and second λ/4 phase difference plates230 and 340 is about 1.35 in thickness directions, and the phase delayvalue Rth of the positive A-plate 240 is about 100 nm in a thicknessdirection.

Referring to FIGS. 9B to 9D, comparing to the previous exampleembodiment of FIG. 3A, for example, when the azimuth angle φ is betweenabout 90 and about 120 degrees and between about 270 and about 300degrees, the light leakage is reduced considerably.

FIG. 9E illustrates a luminance distribution when the phase delay valueΔnd of the liquid crystal layer 140 is about 325 nm at a wavelength ofabout 550 nm, the refractive index nz of the first and second λ/4 phasedifference plates 230 and 340 is about 1.35 in thickness directions, andthe phase delay value Rth of the positive A-plate 240 is about 110 nm ina thickness direction. FIG. 9F illustrates a luminance distribution whenthe phase delay value Δnd of the liquid crystal layer 140 is about 325nm at a wavelength of about 550 nm, the refractive index nz of the firstand second λ/4 phase difference plates 230 and 340 is about 1.35 inthickness directions, and the phase delay value Rth of the positiveA-plate 240 is about 120 nm in a thickness direction.

Referring to FIGS. 9E and 9F, comparing to the previous exampleembodiment of FIG. 3A, when the phase delay value Rth of the positiveA-plate 240 is about 110 nm to about 120 nm in a thickness direction,the luminance was generally less (for example, no more than about 0.010cd/m²) than that of FIG. 3A. That is, the positive A-plate 240 reduceslight leakage in every direction.

FIG. 9G illustrates a luminance distribution when the phase delay valueΔnd of the liquid crystal layer 140 is about 325 nm at a wavelength ofabout 550 nm, the refractive index nz of the first and second λ/4 phasedifference plates 230 and 340 is about 1.35 in thickness directions, andthe phase delay value Rth of the positive A-plate 240 is about 130 nm ina thickness direction. FIG. 9H illustrates a luminance distribution whenthe phase delay value Δnd of the liquid crystal layer 140 is about 325nm at a wavelength of about 550 nm, the refractive index nz of the firstand second λ/4 phase difference plates 230 and 340 is about 1.35 inthickness directions, and the phase delay value Rth of the positiveA-plate 240 is about 140 nm in a thickness direction.

Referring to FIGS. 9E and 9F, comparing to the previous exampleembodiment of FIG. 3A, when the phase delay value Rth of the positiveA-plate 240 is about 130 nm to about 140 nm in a thickness direction,and the azimuth angle φ is between about 0 to 30 degrees and betweenabout 180 to 210 degrees, light leakage is reduced.

As shown in the above luminance distributions, when a compensating filmsuch as the positive A-plate 240 is employed, the light leakage of thedisplay apparatus is reduced as compared to that without thecompensating film. Particularly, when phase delay value Rth of thepositive A-plate 240 is between about 110 nm and about 120 nm in athickness direction, light leakage is maximally reduced. However, theseresults occur when the phase delay value Δnd of the liquid crystal layer140 is about 325 nm at a wavelength of about 550 nm. In differentconditions (e.g., for different phase delay values), results may differ.

According to the present example embodiment, positive A-plate 240 isdisposed between the first polarizer 220 and the first λ/4 phasedifference plate 230, so as to reduce light leakage and improve viewingangle.

FIG. 10 is a cross sectional view illustrating a display apparatusaccording to a further example embodiment of the present invention. FIG.11 is a conceptual diagram illustrating aspects of operation of thedisplay apparatus of FIG. 10.

The display apparatus according to the present example embodiment issubstantially the same as the previous example embodiment of FIG. 1,except that a first polarizing plate 200 further includes a negativeC-plate 250 as a compensating film. Thus, any repetitive explanationconcerning the same or like elements as those described in the previousexample embodiment of FIG. 1 is omitted.

Referring to FIGS. 10 and 11, the first polarizing plate 200 includes afirst protective layer 210, a first polarizer 220, a first λ/4 phasedifference plate 230 and the negative C-plate 250. The second polarizingplate 300 includes a low-reflective film 310, a second protective layer320, a second polarizer 330 and a second λ/4 phase difference plate 340.

The first polarizer 220 is disposed between the first protection layer210 and the negative C-plate 250. The first polarizer 220 has a firstabsorptive axis 220 a substantially parallel with a first direction D1,and a first polarizing axis 220 b substantially parallel with a seconddirection D2. Here, second direction D2 is substantially perpendicularto the first direction D1. The first polarizer 220 includes a firstsurface 221 and a second surface 222 opposite to the first surface 221.

The negative C-plate 250 is disposed over the first surface 221 of thefirst polarizer 220. The negative C-plate 250 includes a compensatingaxis 250 a substantially parallel with the first polarizing axis 220 b.The negative C-plate 250 includes a first surface 251 facing the firstsurface 221 of the first polarizer 220, and a second surface 252opposite to the first surface 251.

The negative C-plate 250 is a phase delay film satisfying nx=ny>nz,where nx is a refractive index in an x direction, ny is a refractiveindex in a y direction substantially perpendicular to the x direction,and nz is a refractive index in a z direction substantiallyperpendicular to both the x and y directions. In the present exampleembodiment, the x direction is substantially perpendicular to the firstdirection D1, and the y direction is substantially perpendicular to thesecond direction D2.

The plane phase delay value Ro of the negative C-plate 250 is determinedby Ro=(nx−ny)*d, where d is the thickness of C-plate 250. Accordingly,as nx=ny, the value of Ro for negative C-plate 250 is about zero.

The phase delay value Rth of the negative C-plate 250 is{(nx+ny)/2−nz}*d in a thickness direction. As nx=ny>nz for the thicknessdirection of C-plate 250, the phase delay value Rth is positive. Thephase delay value Rth of the negative C-plate 250 may preferably bebetween about 30 nm and about 80 nm in a thickness direction.

The first λ/4 phase difference plate 230 is disposed over the secondsurface 252 of the negative C-plate 250. The first λ/4 phase differenceplate 230 has a first delaying axis 230 a inclined by an angle of about45 degrees, or about 135 degrees with respect to the first polarizingaxis 220 b of the first polarizer 220. The first λ/4 phase differenceplate 230 includes a first surface 231 facing the second surface 252 ofthe negative C-plate 250, and a second surface 232 opposite to the firstsurface 231. The second surface 232 of the first λ/4 phase differenceplate 230 is coupled to a second surface 112 of a first substrate 110.

A display panel 100 includes a first substrate 110, a second substrate130 and a liquid crystal layer 140 disposed between the first substrate110 and the second substrate 130. A phase delay value Δnd of the liquidcrystal layer 140 may be from about 275 nm to about 350 nm at awavelength of about 550 nm. For example, the phase delay value Δnd ofthe liquid crystal layer 140 may be about 325 nm. The Δn is ananisotropic refractive index of the liquid crystal layer 140 and d is acell gap of the liquid crystal layer 140.

The second λ/4 phase difference plate 340 is disposed over the displaypanel 100. In detail, the second λ/4 phase difference plate 340 isdisposed over a second surface 132 of the second substrate 130. Thesecond λ/4 phase difference plate 340 has a second delaying axis 340 asubstantially perpendicular to the first delaying axis 230 a. The secondλ/4 phase difference plate 340 includes a first surface 341 facing thesecond surface 132 of the second substrate 130, and a second surface 342facing a first surface 331 of the second polarizer 330.

For the above-described liquid crystal layer 140 with phase delay valueΔnd of about 275 nm to about 350 nm, the first and second λ/4 phasedifference plates 230 and 340 may have a refractive index nz betweenabout 1.35 and about 2.05 in thickness directions.

The second polarizer 330 is disposed over the second surface 342 of thesecond λ/4 phase difference plate 340. The second polarizer 330 has asecond absorptive axis 330 a substantially perpendicular to the firstabsorptive axis 220 a, and a second polarizing axis 330 b substantiallyperpendicular to the second absorptive axis 330 a. The second protectivelayer 320 is attached to the second surface 332 of the second polarizer330.

FIGS. 12A to 12C are graphs illustrating a luminance distribution withrespect to phase delay for the negative C-plate 250 of FIG. 10, and forblack images.

FIG. 12A illustrates a luminance distribution when the phase delay valueΔnd of the liquid crystal layer 140 is about 325 nm at a wavelength ofabout 550 nm, the refractive index nz of the first and second λ/4 phasedifference plates 230 and 340 is about 1.65 in thickness directions, andthe phase delay value Rth of the negative C-plate 250 is about 10 nm ina thickness direction. FIG. 12B illustrates a luminance distributionwhen the phase delay value Δnd of the liquid crystal layer 140 is about325 nm at a wavelength of about 550 nm, the refractive index nz of thefirst and second λ/4 phase difference plates 230 and 340 is about 1.65in thickness directions, and the phase delay value Rth of the negativeC-plate 250 is about 30 nm in a thickness direction. FIG. 12Cillustrates a luminance distribution when the phase delay value Δnd ofthe liquid crystal layer 140 is about 325 nm at a wavelength of about550 nm, the refractive index nz of the first and second λ/4 phasedifference plates 230 and 340 is about 1.65 in thickness directions, andthe phase delay value Rth of the negative C-plate 250 is about 60 nm ina thickness direction.

Referring to FIGS. 12A to 12C, when a polar angle θ is between about 0and about 20 degrees, the luminance was very low (for example, about0.000 cd/m²) for any azimuth angle φ. The luminance generally increasesas the polar angle θ and the phase delay value Rth increase.

Meanwhile, comparing to the previous example embodiment of FIG. 3D whichdoes not employee the negative C-plate 250, when the phase delay valueRth of the negative C-plate 250 is between about 10 nm to about 30 nm ina thickness direction, the luminance distribution is similar to that ofFIG. 3D. However, when the phase delay value Rth of the negative C-plate250 is about 60 nm in a thickness direction, the areas of relativelyhigh luminance are shifted counterclockwise relative to those of FIG.3D. Although not shown in the figures, the shift of the areas ofrelatively high luminance increases as the phase delay value Rth of thenegative C-plate 250 increases. Therefore, it is possible to adjust theluminance distribution to be symmetric for the entire azimuth angle φ.

According to the present example embodiment, the asymmetric viewingangle may be improved to be symmetric by adjusting the phase delay valueRth of the negative C-plate 250 in a thickness direction, thus improvingdisplay quality.

FIG. 13 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention.FIG. 14 is a conceptual diagram illustrating an optical operation of thedisplay apparatus of FIG. 13.

The display apparatus according to the present example embodiment issubstantially the same as the previous example embodiment of FIG. 1,except that a first polarizing plate 200 further includes a positiveA-plate 240 and a negative C-plate 250 as a compensating film. Thus, anyrepetitive explanation concerning the same or like elements as thosedescribed in the previous example embodiments is omitted.

Referring to FIGS. 13 and 14, the first polarizing plate 200 includes afirst protective layer 210, a first polarizer 220, a first λ/4 phasedifference plate 230, positive A-plate 240 and the negative C-plate 250.The second polarizing plate 300 includes a low-reflective film 310, asecond protective layer 320, a second polarizer 330 and a second λ/4phase difference plate 340.

The first polarizer 220 is disposed between the first protection layer210 and the positive A-plate 240. The first polarizer 220 has a firstabsorptive axis 220 a substantially parallel with a first direction D1,and a first polarizing axis 220 b substantially parallel with a seconddirection D2. Here, second direction D2 is substantially perpendicularto first direction D1. The first polarizer 220 includes a first surface221 and a second surface 222 opposite to the first surface 221.

The positive A-plate 240 is disposed over the first surface 221 of thefirst polarizer 220. The positive A-plate 240 includes a compensatingaxis 240 a substantially parallel with the first polarizing axis 220 b.A phase delay value Rth of the positive A-plate 240 may be between about70 nm and about 140 nm in a thickness direction. The positive A-plate240 includes a first surface 241 facing the first surface 221 of thefirst polarizer 220, and a second surface 242 opposite to the firstsurface 241.

The negative C-plate 250 is disposed over the second surface 242 of thepositive A-plate 240. The negative C-plate 250 includes a compensatingaxis 250 a substantially parallel with the first polarizing axis 220 b.A phase delay value Rth of the negative C-plate 250 may be between about30 nm and about 80 nm in a thickness direction. The negative C-plate 250includes a first surface 251 facing the second surface 242 of thepositive A-plate 240, and a second surface 252 opposite to the firstsurface 251.

The first λ/4 phase difference plate 230 is disposed over the secondsurface 252 of the negative C-plate 250. The first λ/4 phase differenceplate 230 has a first delaying axis 230 a inclined by an angle of about45 degrees, or about 135 degrees with respect to the first polarizingaxis 220 b of the first polarizer 220. The first λ/4 phase differenceplate 230 includes a first surface 231 facing the second surface 252 ofthe negative C-plate 250, and a second surface 232 opposite to the firstsurface 231. The second surface 232 of the first λ/4 phase differenceplate 230 is coupled to a second surface 112 of a first substrate 110.

A display panel 100 includes the first substrate 110, a second substrate130 and a liquid crystal layer 140 disposed between the first substrate110 and the second substrate 130. A phase delay value Δnd of the liquidcrystal layer 140 may be from about 275 nm to about 350 nm at awavelength of about 550 nm. For example, the phase delay value Δnd ofthe liquid crystal layer 140 may be about 325 nm. The Δn is ananisotropic refractive index of the liquid crystal layer 140 and d is acell gap of the liquid crystal layer 140.

The second λ/4 phase difference plate 340 is disposed over the displaypanel 100. In detail, the second λ/4 phase difference plate 340 isdisposed over a second surface 132 of the second substrate 130. Thesecond λ/4 phase difference plate 340 has a second delaying axis 340 asubstantially perpendicular to the first delaying axis 230 a. The secondλ/4 phase difference plate 340 includes a first surface 341 facing thesecond surface 132 of the second substrate 130, and a second surface 342facing a first surface 331 of the second polarizer 330.

For the above-described liquid crystal layer 140 with phase delay valueΔnd of about 275 nm to about 350 nm at a wavelength of about 550 nm, thefirst and second λ/4 phase difference plates 230 and 340 may have arefractive index nz between about 1.35 and about 2.05 in thicknessdirections.

The second polarizer 330 is disposed over the second surface 342 of thesecond λ/4 phase difference plate 340. The second polarizer 330 has asecond absorptive axis 330 a substantially perpendicular to the firstabsorptive axis 220 a, and a second polarizing axis 330 b substantiallyperpendicular to the second absorptive axis 330 a. The second protectivelayer 320 is attached to the first surface 331, which is opposite to thesecond surface 332 of the second polarizer 330.

Although the present example embodiment has a positive A-plate 240 isdisposed first, with the negative C-plate 250 disposed thereafter, thestructures should not be limited to the present example embodiment. Forexample, the negative C-plate 250 may be applied first, and the positiveA-plate 240 may be applied second.

FIG. 15 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention.

The display apparatus according to the present example embodiment issubstantially the same as the previous example embodiment of FIGS. 1 to5B, except that the display apparatus is a transmissive type display inwhich display panel 100 is operated in transmissive mode. Thus, anyrepetitive explanation concerning the same or like elements as thosedescribed in the previous example embodiment of FIGS. 1 to 5B isomitted.

Referring to FIG. 15, the display panel 100 includes a first substrate110, a second substrate 130 opposite to the first substrate 110, and aliquid crystal layer 140 disposed between the first substrate 110 andthe second substrate 130.

The first substrate 110 further includes a pixel electrode 120. Thepixel electrode 120 includes a transparent conductive material. Thesecond substrate 130 includes a plurality of color filters (not shown),and a common electrode (not shown) disposed on the color filters. Theliquid crystal layer 140 is disposed between the first substrate 110 andthe second substrate 130. The liquid crystal layer 140 may be driven ina vertical alignment (VA) mode.

The first polarizing plate 200 is attached under the display panel 100.The first polarizing plate 200 may include a first protection layer 210,a first polarizer 220 and a first λ/4 phase difference plate 230.

The first protection layer 210 is disposed under the first polarizer220, so that the first protection layer 210 protects the first polarizer220. The first polarizer 220 also polarizes incident light in a specificdirection. The first λ/4 phase difference plate 230 is disposed betweenthe first substrate 110 and the first polarizer 220. The first λ/4 phasedifference plate 230 delays the light incident from the first polarizer220 by a λ/4 phase. The first λ/4 phase difference plate 230 may have arefractive index nz between about 1.35 and about 2.05 in a thicknessdirection.

The second polarizing plate 300 is attached to the display panel 100.The second polarizing plate 300 may include a low-reflective film 310, asecond protection layer 320, a second polarizer 330 and a second λ/4phase difference plate 340. The low-reflective film 310 is disposed overthe second protection layer 320. The second protection layer 320 isdisposed over the second polarizer 330, so that the second protectionlayer 320 protects the second polarizer 330. The second polarizer 330 isdisposed under the second protection layer 320 to polarize an incidentlight in a specific direction. The second λ/4 phase difference plate 340is disposed between the second substrate 130 and the second polarizer330, and delays the light incident from the second substrate 130 by aλ/4 phase. The second λ/4 phase difference plate 340 may have arefractive index nz between about 1.35 and about 2.05 in a thicknessdirection.

According to the present example embodiment, the low-reflective film 310is disposed over the second polarizer 330, and the second λ/4 phasedifference plate 340 is disposed between the second polarizer 330 andthe second substrate 130 so that glare by the reflection of an externallight a may be prevented. In addition, the refractive indexes of thefirst and the second λ/4 phase difference plates 230 and 340 areadjusted in thickness directions so that light leakage in a side viewmay be reduced. Therefore, the viewing angle of the display apparatusmay be improved.

FIG. 16 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention.

The display apparatus according to the present example embodiment issubstantially the same as the previous example embodiment of FIGS. 6 to9H, except that the display apparatus is a transmissive type display inwhich a display panel 100 is operated in transmissive mode. Thus, anyrepetitive explanation concerning the same or like elements as thosedescribed in the previous example embodiment of FIGS. 6 to 9H isomitted.

Referring to FIG. 16, the display apparatus of the present exampleembodiment includes the display panel 100, a first polarizing plate 200attached under the display panel 100, a second polarizing plate 300attached on the display panel 100 and a backlight unit 400 disposedunder the first polarizing plate 200 to provide light to the displaypanel 100.

The first polarizing plate 200 includes a first protective layer 210, afirst polarizer 220, a first λ/4 phase difference plate 230 and apositive A-plate 240. The second polarizing plate 300 includes alow-reflective film 310, a second protective layer 320, a secondpolarizer 330 and a second λ/4 phase difference plate 340.

The first polarizer 220 is disposed between the first protection layer210 and the positive A-plate 240. The positive A-plate 240 is disposedover the first polarizer 220. The positive A-plate 240 includes acompensating axis substantially parallel with a polarizing axis of thefirst polarizer 220.

A phase delay value Rth of the positive A-plate 240 may be from about 70nm to about 140 nm in a thickness direction. The phase delay value Rthof the positive A-plate 240 is {(nx+ny)/2−nz}*d in a thicknessdirection. The nx is a refractive index in an x direction, the ny is arefractive index in a y direction substantially perpendicular to the xdirection and the nz is a refractive index in a z directionsubstantially perpendicular to both the x and y directions. Here, drepresents a thickness of the positive A-plate 240.

The first λ/4 phase difference plate 230 is disposed over the positiveA-plate 240. The first λ/4 phase difference plate 230 has a delayingaxis inclined by an angle of about 45 degrees, or about 135 degrees withrespect to the polarizing axis of the first polarizer 220.

The second λ/4 phase difference plate 340 is disposed over the displaypanel 100. The second λ/4 phase difference plate 340 has a delaying axisinclined by an angle of about 45 degrees, or about 135 degrees withrespect to a polarizing axis of the second polarizer 330. The delayingaxis of the second λ/4 phase difference plate 340 is substantiallyperpendicular to the delaying axis of the first λ/4 phase differenceplate 230. For a liquid crystal layer 140 having a phase delay value Δndfrom about 275 nm to about 350 nm at a wavelength of about 550 nm, thefirst and second λ/4 phase difference plates 230 and 340 may have arefractive index nz between about 1.35 and about 2.05 in thicknessdirections.

The second polarizer 330 is disposed over the second λ/4 phasedifference plate 340. The second polarizer 330 has the polarizing axissubstantially perpendicular to the polarizing axis of the firstpolarizer 220.

According to the present example embodiment, the positive A-plate 240 isdisposed between the first polarizer 220 and the first λ/4 phasedifference plate 230. The phase delay value Rth in the thicknessdirection of the positive A-plate 240 is adjusted so that the lightleakage in a side view may be reduced. This acts to improve the viewingangle of the display apparatus.

FIG. 17 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention.

The display apparatus according to the present example embodiment issubstantially the same as the previous example embodiment of FIGS. 10 to12C, except that the display apparatus is a transmissive type display inwhich a display panel 100 is operated in transmissive mode. Thus, anyrepetitive explanation concerning the same or like elements as thosedescribed in the previous example embodiment of FIGS. 10 to 12C isomitted.

Referring to FIG. 17, the display apparatus of the present exampleembodiment includes the display panel 100, a first polarizing plate 200attached under the display panel 100, a second polarizing plate 300attached on the display panel 100 and a backlight unit 400 disposedunder the first polarizing plate 200 providing light to the displaypanel 100.

The first polarizing plate 200 includes a first protective layer 210, afirst polarizer 220, a first λ/4 phase difference plate 230 and anegative C-plate 250. The second polarizing plate 300 includes alow-reflective film 310, a second protective layer 320, a secondpolarizer 330 and a second λ/4 phase difference plate 340.

The first polarizer 220 is disposed between the first protection layer210 and the negative C-plate 250. The negative C-plate 250 is disposedover the first polarizer 220. The negative C-plate 250 includes acompensating axis substantially parallel with a polarizing axis of thefirst polarizer 220.

The plane phase delay value Ro of negative C-plate 250 is (nx−ny)*d,where d represents a thickness of the negative C-plate 250. As above,nx=ny for C-plate 250, so that Ro is about zero. A phase delay value Rthof the negative C-plate 250 is positive in a thickness direction. Thephase delay value Rth of the negative C-plate 250 is {(nx+ny)/2−nz}*d ina thickness direction. The phase delay value Rth of the negative C-plate250 may preferably be between about 30 nm and about 80 nm in a thicknessdirection.

The first λ/4 phase difference plate 230 is disposed over the negativeC-plate 250. The first λ/4 phase difference plate 230 has a delayingaxis inclined by an angle of about 45 degrees, or about 135 degrees withrespect to the polarizing axis of the first polarizer 220. The secondλ/4 phase difference plate 340 is disposed over the display panel 100.The second λ/4 phase difference plate 340 has a delaying axis inclinedby an angle of about 45 degrees, or about 135 degrees with respect to apolarizing axis of the second polarizer 330. The delaying axis of thesecond λ/4 phase difference plate 340 is substantially perpendicular tothe delaying axis of the first λ/4 phase difference plate 230. Forliquid crystal layer 140 having a phase delay value Δnd from about 275nm to about 350 nm at a wavelength of about 550 nm, the first and secondλ/4 phase difference plates 230 and 340 may have a refractive index nzbetween about 1.35 and about 2.05 in thickness directions.

The second polarizer 330 is disposed over the second λ/4 phasedifference plate 340. The second polarizer 330 has a polarizing axissubstantially perpendicular to the polarizing axis of the firstpolarizer 220.

According to the present example embodiment, the negative C-plate 250 isdisposed between the first polarizer 220 and the first .lamda./4 phasedifference plate 230, and the phase delay value Rth of the negativeC-plate 250 is adjusted so that the viewing angle may be made diagonallysymmetric. This acts to improve display quality.

FIG. 18 is a cross sectional view illustrating a display apparatusaccording to still another example embodiment of the present invention.FIG. 19 is a conceptual diagram illustrating operation of the displayapparatus of FIG. 18.

The display apparatus according to the present example embodiment issubstantially the same as the previous example embodiment of FIG. 13,except that the display apparatus is a transmissive type display inwhich a display panel 100 is operated in transmissive mode, and thepositions of positive A-plate and negative C-plate differ. Thus, anyrepetitive explanation concerning the same or like elements as thosedescribed in the previous example embodiment of FIG. 13 is omitted.

Referring to FIGS. 18 and 19, the first polarizing plate 200 includes afirst protective layer 210, a first polarizer 220, a first λ/4 phasedifference plate 230, the positive A-plate 240 and the negative C-plate250. The second polarizing plate 300 includes a low-reflective film 310,a second protective layer 320, a second polarizer 330 and a second λ/4phase difference plate 340.

The first polarizer 220 is disposed between the first protection layer210 and the negative C-plate 250. The first polarizer 220 has a firstabsorptive axis 220 a substantially parallel with a first direction D1,and a first polarizing axis 220 b substantially parallel with a seconddirection D2. Here, second direction D2 is substantially perpendicularto the first direction D1. The first polarizer 220 includes a firstsurface 221 and a second surface 222 opposite to the first surface 221.

The negative C-plate 250 is disposed over the first surface 221 of thefirst polarizer 220. The negative C-plate 250 includes a compensatingaxis 250 a substantially parallel to the first polarizing axis 220 b. Aphase delay value Rth of the negative C-plate 250 may be between about30 nm and about 80 nm in a thickness direction. The negative C-plate 250includes a first surface 251 facing the first surface 221 of the firstpolarizer 220, and a second surface 252 opposite to the first surface251.

The positive A-plate 240 is disposed over the second surface 252 of thenegative C-plate 250. The positive A-plate 240 includes a compensatingaxis 240 a substantially parallel with the first polarizing axis 220 b.A phase delay value Rth of the positive A-plate 250 may be between about70 nm and about 140 nm in a thickness direction. The positive A-plate240 includes a first surface 241 facing the second surface 252 of thenegative C-plate 250, and a second surface 242 opposite to the firstsurface 241.

The first λ/4 phase difference plate 230 is disposed over the secondsurface 242 of the positive A-plate 240. The first λ/4 phase differenceplate 230 has a first delaying axis 230 a inclined by an angle of about45 degrees, or about 135 degrees with respect to the first polarizingaxis 220 b of the first polarizer 220. The first λ/4 phase differenceplate 230 includes a first surface 231 facing the second surface 242 ofthe positive A-plate 240, and a second surface 232 opposite to the firstsurface 231. The second surface 232 of the first λ/4 phase differenceplate 230 is coupled to second surface 112 of the first substrate 110.

A display panel 100 includes the first substrate 110, a second substrate130, and a liquid crystal layer 140 disposed between the first substrate110 and the second substrate 130. A phase delay value Δnd of the liquidcrystal layer 140 may be from about 275 nm to about 350 nm at awavelength of about 550 nm. For example, the phase delay value Δnd ofthe liquid crystal layer 140 may be about 325 nm. The quantity Δn is ananisotropic refractive index of the liquid crystal layer 140, and d is acell gap of the liquid crystal layer 140.

The second λ/4 phase difference plate 340 is disposed over the displaypanel 100. In detail, the second λ/4 phase difference plate 340 isdisposed over a second surface 132 of the second substrate 130. Thesecond λ/4 phase difference plate 340 has a second delaying axis 340 asubstantially perpendicular to the first delaying axis 230 a. The secondλ/4 phase difference plate 340 includes a first surface 341 facing thesecond surface 132 of the second substrate 130, and a second surface 342facing a first surface 331 of the second polarizer 330.

For liquid crystal layer 140 having a phase delay value Δnd from about275 nm to about 350 nm in a wavelength of about 550 nm, the first andsecond λ/4 phase difference plates 230 and 340 may have a refractiveindex nz between about 1.35 and about 2.05 in thickness directions.

The second polarizer 330 is disposed over the second surface 342 of thesecond λ/4 phase difference plate 340. The second polarizer 330 has asecond absorptive axis 330 a substantially perpendicular to the firstabsorptive axis 220 a, and a second polarizing axis 330 b substantiallyperpendicular to the second absorptive axis 330 a. The second protectivelayer 320 is attached to the first surface 331, which is opposite to thesecond surface 332 of the second polarizer 330.

In this exemplary embodiment, the negative C-plate 250 is disposedfirst, and the positive A-plate 240 is disposed thereafter. However, theinvention is not limited to the present example embodiment. For example,the positive A-plate 240 may be disposed first, and the negative C-plate250 may be disposed later.

According to various example embodiments of the present invention, firstand second λ/4 phase difference plates are disposed over and under adisplay panel, and refractive indexes of the λ/4 phase difference platesare adjusted so as to reduce light leakage in side views. In addition, acompensating film compensating phase difference of a liquid crystallayer can be disposed between a first polarizer (which is disposed underthe display panel) and the first λ/4 phase difference plate. Thepresence of the compensating film reduces light leakage in a side view,and improves viewing angle symmetry. In particular, viewing angle may bemade diagonally symmetric. In these respects, embodiments of theinvention act to improve display quality.

Although the exemplary embodiments of the present invention have beendescribed, it is understood that the present invention should not belimited to these exemplary embodiments but various changes andmodifications can be made by one ordinary skilled in the art within thespirit and scope of the present invention as hereinafter claimed.

What is claimed is:
 1. A polarizing plates set comprising: a first linear polarizer having a first linear polarizing axis extending in a first lateral direction, the first lateral direction being part of a lateral plane also having a second lateral direction different from the first lateral direction; a first λ/4 phase difference plate disposed over the first polarizer and having a refractive index (nz) between about 1.35 and about 2.05 in a thickness direction thereof, the thickness direction being orthogonal to the lateral plane; a second linear polarizer having a second linear polarizing axis extending in the second lateral direction, the second polarizer being disposed above and spaced apart from the first linear polarizer and also from the first λ/4 phase difference plate; and a second λ/4 phase difference plate disposed under the second polarizer, above the first λ/4 phase difference plate, and having a refractive index (nz) in a thickness direction of the second λ/4 phase difference plate which is essentially the same as that of the first λ/4 phase difference plate, wherein the refractive index (nz) of the first and second λ/4 phase difference plates is between about 1.65 and about 1.75.
 2. The polarizing plates set of claim 1, further comprising a first compensating film disposed between the first polarizer and the first λ/4 phase difference plate.
 3. The polarizing plates set of claim 2, wherein the first compensating film is a positive A-plate, and a phase delay value of the positive A-plate is between about 70 nm and about 140 nm in a thickness direction.
 4. The polarizing plates set of claim 2, wherein the first compensating film is a negative C-plate, and a phase delay value of the negative C-plate is between about 30 nm and about 80 nm in a thickness direction.
 5. A display apparatus comprising: a display panel comprising: a first substrate including a pixel electrode; a second substrate opposite to the first substrate; and a liquid crystal layer disposed between a first surface of the first substrate and a first surface of the second substrate; a first polarizing plate comprising: a first polarizer disposed under a second surface of the first substrate and having a first polarizing axis; and a first λ/4 phase difference plate disposed between the second surface of the first substrate and the first polarizer and having a refractive index between about 1.35 and about 2.05 in a thickness direction; and a second polarizing plate comprising: a second polarizer disposed over a second surface of the second substrate and having a second polarizing axis crossing the first polarizing axis; and a second λ/4 phase difference plate disposed between the second surface of the second substrate and the second polarizer and having a refractive index which is essentially the same as that of the first λ/4 phase difference plate in a thickness direction, wherein the refractive index (nz) of the first λ/4 phase difference plate and the second λ/4 phase difference plate is between about 1.65 and about 1.75.
 6. The display apparatus of claim 5, wherein a phase delay value of the liquid crystal layer is from about 275 nm to about 350 nm at a wavelength of about 550 nm.
 7. The display apparatus of claim 6, wherein the first polarizing plate further comprises a compensating film disposed between the first polarizer and the first λ/4 phase difference plate so as to compensate for a phase difference generated by the liquid crystal layer.
 8. The display apparatus of claim 7, wherein the compensating film is a positive A-plate, and a phase delay value of the positive A-plate is between about 70 nm and about 140 nm in a thickness direction.
 9. The display apparatus of claim 7, wherein the compensating film is a negative C-plate, and a phase delay value of the negative C-plate is between about 30 nm and about 80 nm in a thickness direction. 